A disclosed passenger protection device in a motor vehicle with an airbag module which is mounted behind a wall area and contains at least one folded airbag and at least one gas generator (DE 196 17 758 C1) comprises a covered exit opening in the wall area which may be opened by application of pressure for the airbag which is opened after activation.
The exit opening is covered in this instance by a cover cap which may be lifted from a closed position to a clearing position permitting emergence of the airbag opening under pressure. In addition, a rebound strap mounting is provided for the cover cap. The cover cap may in this instance be forced out of an airbag cover in the wall area enclosing the cover cap. In order to enlarge this opening predetermined yield lines are provided which extend more or less radially from the airbag exit opening in the wall area. The movement of a cover cap which has been forced out and lifted is relatively uncontrolled in the area delimited by the length of the rebound strap, as a result of which these cover caps may exhibit greater aggressive behavior toward a vehicle passenger. A relatively large opening diameter is required for the purpose of airbag emergence, a diameter which is unimpeded to the greatest extent possible, with the result that the removable cover cap will accordingly also be relatively large in diameter. Consequently, freedom of configuration is constrained toward smaller diameters for the cover caps such as are required, for example, in the steering wheel hub area in the case of a steering wheel airbag. But it is also to be noted in this connection that smaller lift-offcover caps may additionally exhibit more aggressive behavior toward a passenger.
A similar design is also disclosed by DE 40 10 767 A1.
DE 197 49 914 A1 also discloses a passenger protection device on a steering wheel of a vehicle with a steering wheel airbag module, the steering wheel airbag module being mounted behind a hub cover of a steering wheel hub and containing at least one folded steering wheel airbag and at least one gas generator. The hub cover has a stationary center area as first wall area around which is mounted a second wall area immediately adjacent to an edge connecting area. A predetermined circular yield line mounted concentrically with the stationary center area is provided in the second wall area, spaced a certain distance from the stationary center area and thus spaced a certain distance from the edge connection area. In addition, there is formed in the second wall area a plurality of radially extending predetermined opening lines which extend radially from the edge connection area of the second wall area into an area over the predetermined opening line moving in a circle, so that individual flap areas are formed on the hub cover. In the event of airbag activation, the airbag inflating in a circle around the stationary center area exerts pressure from below on the second wall area such that the individual predetermined opening lines move apart and so clear an annular gap around the stationary center area for airbag emergence. The second wall area moves apart in such a way that the annular gap is formed at a certain distance from the stationary center area more or less in the area of the predetermined opening line by the individual opening flap areas.
With a design such as this a removable cover flap may be eliminated, since the wall area enclosed in the annular gap may remain stationary as center area. The hub cover is in this instance made of a plastic material making it possible to provide the individual predetermined yield points of the predetermined opening lines on the inside of the cover so as not to be visible from the exterior. However, a design such as this of the hub cover with predetermined opening lines is possible only with certain plastic materials. In particular, in the case of high-quality vehicle interior equipment the desire still exists for use of other high-quality materials such as leather, textile or fabric material, etc. in conjunction with the design of steering wheel covers and so hub covers. However, a problem arises with such high-quality materials, in that in this instance predetermined opening lines or predetermined yield points are undesirably visible from outside, that is, from the visible side. This leads to an impression altogether of lower quality and so lowers the overall optical impression, especially in the case of high-quality vehicle interior accouterments. In addition, the cover is possibly also damaged as a result. Consequently, a design such as this of a passenger protection device on a steering wheel with such predetermined opening lines is scarcely workable when use is made of the materials in question for hub and steering wheel covers and so the potential for their use can only be restricted.
In addition, such production of predetermined opening lines by means of individual predetermined yield points also entails considerable cost for production engineering, so that production is also relatively expensive in the aggregate.
A passenger protection device on a steering wheel of a vehicle in which a plurality of different materials, in particular also high-quality leather and/or fabric materials, may be used as hub and/or steering wheel covers is disclosed in generic WO 97/43783. In the case of this passenger protection device a steering wheel airbag module is mounted behind a hub cover of a steering wheel hub and has at least one folded steering wheel airbag and at least one gas generator. The hub cover has a stationary center area as first wall area around which is mounted a second edge area with immediately adjoining edge connection area. In the event of airbag activation an annular gap may he formed around the stationary center area in the second wall area, the steering wheel airbag being correspondingly circular with a tubular area associated with the annular gap and emerging from it when the bag is in the inflated state. The annular gap may in the event of airbag activation be formed immediately around the stationary center area through expansion and/or opening at least of the edge connection area of the second wall area.
Specifically, in this instance the edge connection area of the second wall area rests against the stationary center area from below, that is, the edge connection area of the second wall area is overlapped by an edge area of the stationary center area. When the airbag is activated, the inflating airbag presses the second wall area, and especially the edge connection area, outward and so away from the configuration connection below the stationary center area for clearing of the annular gap. In this configuration, if the passenger protection device has not been activated the danger exists that as a result of improper treatment, such as pushing on the area of the second wall area, the second wall area will be raised by the stationary center area and undesired access to the area of the airbag or the airbag module is cleared as a result. In addition, a certain undesirable danger of manipulation is also created, especially if the second wall area is made of a material which is relatively flexible.
A similar configuration with the same disadvantages is also disclosed in U.S. Pat No. 4,828,286, in which the edge connection area of the second wall area rests on the edge area of the stationary center area.